Comfort eating, that is eating induced by negative affect, has been a core theme of explanations for overeating and obesity. Psychobiological explanations and processes underlying comfort eating are examined, as well as its prevalence in clinical and nonclinical populations, to consider who may be susceptible, whether certain foods are comforting, and what the implications for treatment may be. Comfort eating may occur in a substantial minority, particularly in women and the obese. Human and animal theories and models of emotional or stress-induced eating show some convergence, and may incorporate genetic predispositions such as impulsivity and reward sensitivity, associated with dopamine dysregulation underlying incentive salience. Comfort eaters show vulnerability to depression, emotional dysregulation and a need to escape negative affect and rumination. During negative affect, they preferentially consume sweet, fatty, energy-dense food, which may confer protection against stress, evidenced by suppression of the hypothalamic–pituitary–adrenal axis response, although activation of the hypothalamic–pituitary–adrenal axis may itself drive appetite for these palatable foods, and the risk of weight gain is increased. Benefits to mood may be transient, but perhaps sufficient to encourage repeated attempts to prolong mood improvement or distract from negative rumination. Cognitive behavioural treatments may be useful, but reliable drug therapy awaits further pharmacogenomic developments.